Semi-conductor devices and the manufacture thereof

ABSTRACT

Unequal diameter pinheads, soldered to silicon chip, so that etch produces chamfered diode.

0 United States Patent us] 3,656,228 Glass [4 1 Apr. 18, 1972 [s41SEMI-CONDUCTOR DEVICES AND THE [56] References Clted MANUFACTURE THEREOFUNITED STATES PATENTS ml Glass England 2,879,190 3/1959 Logan :1 al...29/576 [73] Assignee; Westinghouse Brake and Signal Company 2,993,1557/l96l Galzberger ..29/576 Limited 3, l40,527 7/l964 Valdman et al..29/580 3,154,450 l0/I964 Hoechelman et al 156M? [221 PM; w 15,3,233,305 2/!966 om ..29/576 21 L N I: 884 3,260,634 7/1966 Clark..l56/l7 l 1 App 66 3,288,662 11/1966 Weisberg ..29/57s Related US.Application Data J h F C be" [63] Continuation Of Ser. NO. 688,395. Dec.6, 1967, abang g 3:12 Lazarus doned' Anarney-Larson, Taylor & Hinds [30]Foreign Application Priority Data 57] ABSTRACT 1967 Great Britain"4382/67 Unequal diameter pinheads, soldered to silicon chip, so thatetch produces chamfered diode. [52] US. Cl ..29/578,29/580,29/589,156/17 [51] Int. Cl ..B0lj l7/00, HOll 5/00 [58] Field of Search 29/578,590, 591, 580, 576, 6 Claims, 2 Drawing Figures SEMI-CONDUCTOR DEVICESAND THE MANUFACTURE THEREOF This is a continuation of US. Pat. Ser. No.688,395, filed Dec. 6, 1967.

This invention relates to semi-conductor devices and the method ofmanufacture thereof.

The present invention provides a method of manufacturing asemi-conductor device, which method includes the steps of mounting oneon each of two opposed faces of a semi-conductor element having thereina P-N junction, a pair of terminal members or contacts each of which hasa face adjacent the respective one of the two opposed faces of theelement, said face of one of the contacts being of lesser area than saidface of the other of the contacts and said faces of the two contactsboth being of no greater dimension in any direction than the dimensionin the corresponding direction of the face of the element adjacent whichit is, and thereafter etching away material from the semi-conductorelement from areas thereof not covered by the contacts to provide thesemi-conductor element with a peripheral face which extends between thetwo contacts and slopes inwardly of the element from the contact havingsaid face of larger area to the contact having said face of smallerarea, the periphery of the P-N junction then lying on said peripheralface.

The said faces of the pair of terminal members or contacts may each becircular, the diameter of the face of lesser area being less than thediameter of the face of greater area and the faces being arrangedco-axially, and after the etching away of the material, the peripheralface is frustro-conical.

The zone of the element of that side of the P-N junction adjacent thecontact having the face of lesser area may have a relatively highresistivity to that of the zone of the element on that side of the theP-N junction adjacent the other of the contacts.

The angle between the peripheral face and said face of larger area ofthe two contacts may be less than 60.

The contacts may be of silver.

The element may have deposited thereon an alloy which includes nicholand gold, the contacts subsequently being soldered to the alloy.

The present invention further provides a semi-conductor devicemanufactured in accordance with the above designed methods.

One embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying drawing of which:

FIGS. la to le illustrate various steps in the method of manufacture ofa semi-conductor device, and

FIG. 2 shows a cross sectional view of a device manufactured inaccordance with the method illustrated in FIG. 1.

It will be appreciated that in nonnal manufacturing techniques the stepsillustrated in FIGS. la to 1d inclusive are normally carried out on alarge crystal of semiconductor material which is subsequently dividedinto the chips" or pellets such as is shown, but for the sake of clarityonly a single pellet is shown.

There is shown in FIG.la a pellet 1 of intrinsically N type silicon intowhich phosphorus is diffused in a furnace to form the N+ type layers 2with a layer 3 of intrinsic N type material remaining unchanged in thecenter of the pellet l as illustrated. On one surface the N+ typematerial is subsequently lapped off as shown in FIGJb.

A P+ type layer 4 as shown in FlG.lc is then formed in the pellet l bydiffusing Boron into the surface 5 of the N type layer 3 to form a PNjunction 10. The Boron will not penetrate the N-ltype layer 2 since whenthis layer is formed a layer of phosphosilicate glass is deposited n thesurface 6 of the layer 2 through which the Boron cannot penetrate.

The surfaces 5, 6 of the pellet l are then cleaned to remove anydeposits such as the phosphosilicate glass before a layer 7 of an alloycontaining nickel and gold is deposited thereon by a known techniquesuch as plating, as shown in FlG.ld. Terminal members 8 and 9, which inthe present embodiment are of silver, are then soldered in a furnace tothe layer 7 of nickel/gold allpg (FlGJe).

The evlce us formed 18 sub ected to an etching process which removes thesilicon from the portion of the pellet l which is not covered by theterminal members 8, 9, to produce the device illustrated in FIG. 2.

In such devices it is desirable to have a chamfered peripheral face inthe region of the PN junction to increase the surface breakdown voltageof the device. In order to obtain the desired characteristics it isnecessary that the resistivity of the material on the side of the PNjunction nearer to the larger surface is lower than the resistivity onthe side of the PN junction nearer to the smaller surface.

In the specific embodiment, therefore, the P+ layer 4 is of relativelylow resistivity, the N type layer 3 is of relatively high resistivityand the angle between the terminal member 9 on the peripheral face ofthe element is less than 60.

It is, therefore, necessary before the terminal members 8, 9 are securedto the pellet 1 that a polarity check be made to ensure that the smallertenninal member 8 is secured to the pellet on the side of the N+ typelayer 2, and the larger terminal member 9 on the side of the P+ typelayer 4.

The device is finally completed with a coating of a protective materialsuch as varnish, resin or rubber.

I claim:

1. A method of manufacturing semi-conductor device, which methodincludes the steps of forming a discrete semiconductor pellet from acrystal of semi-conductor material by dividing said crystal of materialinto a plurality of said discrete pellets, said pellet having therein aP-N junction lying between two opposed faces thereof, subsequentlymounting, one on each of two opposed faces of said semi-conductorpellet, a pair of electrical terminal members and associated leads, eachsaid terminal member having a face adjacent the respective one of thetwo opposed faces of the pellet, said face of one of the terminalmembers being of lesser area than said face of the other of the terminalmembers and said faces of the two terminal members both being of nogreater dimension in any direction than the dimension in thecorresponding direction of the adjacent face of the pellet is, andthereafter etching away material from the semi-conductor pellet fromareas thereof not covered by the tenninal members to provide thesemi'conductor pellet with a peripheral face which extends between thetwo terminal members and slopes inwardly of the element from theterminal member having said face of larger area to the terminal memberhaving said face of smaller area, the periphery of the P-N junction thenlying on said peripheral face.

2. A method as claimed in claim 1, wherein the said faces of the pair ofelectrical terminal members are each circular, the diameter of the faceof lesser area being less than the diameter of the face of greater area,said faces being arranged co-axially and, after the etching away of thematerial, said peripheral face of said element being frustro-conical.

3. A method as claimed in claim I wherein the zone of the element onthat side of the P-N junction adjacent the terminal member having theface of lesser area has a relatively high resistivity as compared withthe zone of the element on that side of the P-N junction adjacent theother of the terminal members.

4. A method as claimed in claim I, wherein after the etching away ofmaterial, the angle between peripheral face and the face of larger areaof the two terminal members is less than 60.

5. A method as claimed in claim 1 wherein the terminal members areconstructed of silver.

6. A method as claimed in claim 1 wherein the element has depositedthereon an alloy which includes nickel and gold, the terminal memberssubsequently being soldered to the alloy.

I I t t t

1. A method of manufacturing semi-conductor device, which methodincludes the steps of forming a discrete semi-conductor pellet from acrystal of semi-conductor material by dividing said crystal of materialinto a plurality of said discrete pellets, said pellet having therein aP-N junction lying between two opposed faces thereof, subsequentlymounting, one on each of two opposed faces of said semi-conductorpellet, a pair of electrical terminal members and associated leads, eachsaid terminal member having a face adjacent the respective one of thetwo opposed faces of the pellet, said face of one of the terminalmembers being of lesser area than said face of the other of the terminalmembers and said faces of the two terminal members both being of nogreater dimension in any direction than the dimension in thecorresponding direction of the adjacent face of the pellet is, andthereafter etching away material from the semi-conductor pellet fromareas thereof not covered by the terminal members to provide thesemi-conductor pellet with a peripheral face which extends between thetwo terminal members and slopes inwardly of the element from theterminal member having said face of larger area to the terminal memberhaving said face of smaller area, the periphery of the P-N junction thenlying on said peripheral face.
 2. A method as claimed in claim 1,wherein the said faces of the pair of electrical terminal members areeach circular, the diameter of the face of lesser area being less thanthe diameter of the face of greater area, said faces being arrangedco-axially and, after the etching away of the material, said peripheralface of said element being frustro-Conical.
 3. A method as claimed inclaim 1 wherein the zone of the element on that side of the P-N junctionadjacent the terminal member having the face of lesser area has arelatively high resistivity as compared with the zone of the element onthat side of the P-N junction adjacent the other of the terminalmembers.
 4. A method as claimed in claim 1, wherein after the etchingaway of material, the angle between peripheral face and the face oflarger area of the two terminal members is less than 60* .
 5. A methodas claimed in claim 1 wherein the terminal members are constructed ofsilver.
 6. A method as claimed in claim 1 wherein the element hasdeposited thereon an alloy which includes nickel and gold, the terminalmembers subsequently being soldered to the alloy.